With reference to FIG. 1, a conventional thin flip chip package structure 10 comprises a substrate 11, a chip 12, a dam 13, a sealing resin 14 and a heat dissipation paste 15. The substrate 11 comprises a top surface 11a, a bottom surface 11b, and a through hole 11c penetrating the top surface 11a and the bottom surface 11b. The chip 12 disposed on the top surface 11a of the substrate 11 is electrically connected with the substrate 11 and comprises a plurality of bumps 12a. The dam 13 is formed on the top surface 11a of the substrate 11 and located at outside of the through hole 11c. The sealing resin 14 is formed on the top surface 11a of the substrate 11, and the bumps 12a are covered by the sealing resin 14. The through hole 11c is filled with the heat dissipation paste 15. The dam 13 may be utilized to block the sealing resin 14 to prevent the sealing resin 14 from flowing into the through hole 11c of the substrate 11 to pollute the heat dissipation paste 15. However, an overhigh dam 13 makes the bumps 12a of the chip 12 difficult to connect with the substrate 11 smoothly. On the contrary, once the height of the dam 13 is insufficient, a gap (not shown in Figs.) between the dam 13 and the chip 12 is formed and enables the sealing resin 14 to flow from the gap to the through hole 11c of the substrate 11 therefore polluting the heat dissipation paste 15.